Induction motor



June 22 1926.

C. l. HALL INDUCTION MOTOR Filed June 20 1924 r r mf n t Z A s ,w H 6 25,0 flu w P! A Patented June 22,1926.

CHESTER I. BALL, FORT WAYNE, INDIANA, ASSIGNOR TO GENERAL ELECTRICCOMPANY, CORPORATION OF NEW YORK.

mnucrron' MOTOR.

Application filed June 20, 1924. Serial No. 721,322.

My invention relates to improvements in electric motors of the inductiondisc type.

One object of my invention is to provide an induction disc motor ofimproved mechanical construction. Another object is to increase thetorque and speed of this type of motor, and another object is todecrease the magnetic hum incident to this type of motor.

Although the novel features of my invention a e generally applicable toinduction disc motors, the motor is particularly applicable for drivingphonographs and the invention will be explained as for such use.

In carrying my invention into effect, I make the magnetic circuit of themotor from a light skeleton casting which constitutes the frameworkfor'the motor. The shifting magnetic flux is produced by a plurality ofshading coils per. pole so arranged as to obtain an unusually largedistortion of the flux which cuts the disc. This distortion is furtherincreased and the useless flux which ordinarily cuts the disc isdecreased to a minimum by means of a novel magnetic shunt which divertsa portion of the flux away from the disc after it has passed through theshading coils. The result is that the flux that cuts the disc is veryefiiciently used in producing torque and has an unusually smallcomponent perpendicular to the disc which decrease" the tendency of thedisc to hum due to the magnetic pulsations therethrough.

The features of my invention which are believed to be novelandpatentable will be pointed out in the claims appended hereto. or abetterunderstanding of my invention reference is made in the followingdescription to the accompanying drawings in which Fig. 1 shows a planview of the lower portion of the motor, the upper section of themagnetic framework being removed and a portion of the disc being cutaway to better expose the parts; Fig.2 represents a cross section of themotor taken on line 2-2 of Fig. 1; and Fig. 3 illustrates by way ofcomparison. the difference between a, shaded pole having a single shadedcoil ,and one having a plurality of shading coils arranged according tomy invention.

Referring now to Figs. 1 and 2, .in'the present embodiment I haverepresented the motor as being designed to drive anordinary disc typephonograph. The framework and magnetic circuit of the motor comprise twoannular castings 10 and 11 arranged to fit together like the base andcover of a cylindrical box. The base portion has three integral polepieces 12 rising from the skeleton floor and symmetrically arranged 'atthe same distance from the center thereof. In the center of the floor isa step bearing 13 which supports the vertical shaft 14. The shaft 14carries a worm wheel 15 for driving an adjustable speed governor 16which is suit-ably supported in bearing lugs 17 and 18 integral with thecasting 10. The shaft 14 also carries "the induction disc armature 19and passes through a guide bearing 20 in the center of the upper casting11.

The contacting surfaces of the castin 10 and 11 are machined and flangedas illustrated at 21 so as to fit together accurately and the twosections are held together by three screws, one of which is shown at 22.Lugs 23 are provided on the inner'wall of the casting 10 to receivethese screws. Thev I upper casting has three integral pole pieces 24depending from its lower side in alinement with the pole pieces 12rising from the base and the disc 19, which is preferably made ofcopper, is arranged to rotate in the narrow air gaps thus formed.

The pole pieces 12 are preferably made hollow as illustrated so as todecrease the weight of the motor. The three pole pieces 12 are providedwith energizing coils 25 and these three coils may either be connectedin series or in parallel across the line. Preferably the three coilswill be connected so as to simultaneously produce fluxes in the samedirection. This connection and symmetrical arrangement of the polepieces is in accord ance with the invention described and claimed in mycopending application Serial No. 639,895, filed May 18, 1923, entitledElectric drive for phonographs. This arrangement is such that the forceswhich are perpendicular to the disc and which are produced by thecurrents set up in the disc reacting against the magnetic fieldstherequally balanced with respect through are e to the center line ofthe shaft 14, Consequently, there can be no resultant force which tendsto tip the disc first in one direction and then in another direction. Asmore fully explained in my prior application, this arrangementsubstantially eliminates noise and vibration if the disc is madesufiieiently thick to resist bending by the forces in question.

B my present invention I have materially reduced the forces which areperpen dicular to the disc and at the same time increased the drivingtorque. Consequently,

1 it is not so essential that the disc be made V solid tops of the polepieces 12.v The slots in which the shading coils are contained dividethe pole face into four sections, A, B, C, and D, section A beingunshadcd. section B being shaded by one coil, sgction C shaded by twocoils, and section D by all three coils. Since each shading coildisplaces the flux whichit encircles, it will be seen that the flux insection B lags behind the unshaded flux in section A; that in section Clags behind that in section B and that in section D lags behind that insection C, thus producing a progressive phase displacement of motor, andtherefore its efiiciency, for two reasons; first, the torque isincreased over the single shading coil construct-ion because of the factthat the individual poles corresponding to A, B, C, and D are broughtcloser together giving a shorter effective dis tance between poles fortorque reactions; and second, the speed is increased because the totalpole displacement is increased;

therefore the shifting field actually travels a greater distance duringeach cycle. This reasoning may be made clear by referring to the diagramin Fig. 3. In this figure 12 and 12 represent two poles, the firsthaving a single shaded section B and the second three shaded sectionsB,C, and D. It will be clearly seen that the pole displacements PP, inthe single shaded pole is much less than in the multiple shaded pole.From this point of view, it will be seen that during one cycle the fluxshifts a greater distance int-he multiple shaded pole and thereforecauses a higher speed of rotation of the disc.

Considering the diagram from the point of view of standstill torque, itis seen that the poles must react on poles in the disc through adistance proportional PP, in i2".

' If the shaded part P, be split up into smaller units placed closetogether as B, G, and D in pole 12 while the pole area and total shaded.

- coil sections are maintained constant, the

torque will be increased since the total flux 'view of disc vibrations.

will remain constant while theindividual poles will be closer together.Due to the fact that the attraction varies inversely as the square ofthe distance, the increased spacing between P and P, in pole 12 is morethan compensated for by the much shorter spacing between theintermediate poles cor responding to A, B, C, and D.

The provision of a plurality of displaced individual shading coils asabove described constitutes an important improvement in this type ofmotor. I have further improved the motor by the provision of a magneticshunt 28. It will be seen from an inspection of Figs. land. 2 that thesolid portions of the pole pieces extend slightly above the shadingcoils so as magnetic shunt 28 secured between the trailingpole tip andthe side wall of the casting 10. This shunt is made of soft iron and ispreferably keyed into the part D of the pole piece and secured to theframe 10 by means of a screw 29 threaded into a lug 30 in the wall 10.This shunt thus connects the part D of the pole piece above the shadingcoils with the lower casting forming a parallel path for a portion ofthe main coil flux which does not cut the copper disc 19. All of theflux which traverses this shunt circuit is effective in creatingcurrents in all three shading coils which in turn causes a greater phasedisplacement of the flux cutting the- Without the shunt, the currents inthe shading coils must be induced by flux which cuts the disc and Whilethe resultant shading coil-effect will be greater than with a singleshading coil, it will be less than with the shunt for two reasons;first, the shunt increases the total useful flux because it decreasesthe resultant-reluctance of the flux circuit which is now partiallyacross the air gap cutting the disc and partially through the shunttreading all the shading coils; and second, while the flux cutting thedisc is not greatly reduced, it is progressively lagged to a greaterextent than before because of the increased current in all the shadingcoils. The resultant direction of the force acting upon the disc due tothe reaction between the flux cutting the disc and the currents set upby this flux is now more nearly parallel to the disc and increases therotative torque and efliciency of the motor and decreases the componentof force perpendicular to the disc which is not effective in producingtorque and which is detrimental from the point of It may be stated thatthe resultant effect of this arrangement is to shunt a large proportionof the detrimental component of the flux from the disc which is notefiective in producing torque at the same time increasing the torquecreative the flux which cuts the disc is more efiective to cooperate\vitha small in creating torque than with the usual shading coilarrangement, the amount of flux nece'ssary to cut the disc may bedecreased proportionall which, in turn, has the beneficial result inecreasing the tendency of the disc to vibrate and hum. To obtain thebest results, the character of the shunt 28 should be properlyproportioned to the remainder of the design in any particular case. For

through which said armature is arranged example, if'the air gap throughwhich the disc rotates is increased, the reluctance of the shunt shouldbe increased, for instance, by decreasing its cross section or itspermeability.

'In accordance with the provisions of the patent statutes, I havedescribed the principle of operation of my invention, together with theapparatus which I now consider to represent the best embodiment thereof;but I desire to have it understood that the apparatus shown anddescribed is only illustrative and that the invention may be carried outby other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An induction motor having a rotatably mounted armature of conductingmaterial, a magnetic member having an air ap to rotate, an energizingwinding for said magnetic member, and a plurality of individual shadingcoils on said member adjacent said air gap for producing a progressiveshifting of the flux in the air gap.

2. An induction motor having a rotatably mounted armature of conductingmaterial, a magnetic member having cooperating pole faces on oppositesides of said armature for one of said producing an alternating fluxtherethrough, 40

an energizing winding for said magnetic member, and a plurality ofindividual shading coils arranged one within the other on pole faces forproducing a pro-.'

gressive shi armature.

3. An induction motor having a rotatably mounted disc armature, amagnetic member provided with an air gap through which said armature isarranged to rotate, an energizing winding on said magnetic member forproducing an alternating flux through said air gag transversely of saiddisc armature, a s a ing coil on said magnetic member adjacent the airand means for diverting a portion 0 t e flux threading only said shadingcoil away from the air ting of the flux throughsaid up. y g 4. Aninduction motor having a rotatably mounted armature of conductingmaterial, a mag'petic member provided with an air gap t rough which saidarmature is arran (1 to rotate, an energizing winding for sai magneticmember for producing an alternating flux. through the air gap, aplurality of shading coils on said ma etic member'adjacent the air gapfor prmfiibing a progressive shifting of the flux in the air gap' and amagnet shunt for diverting a portion of the flux threading all of saidshading coils away from the air gap.

5. An induction motor having a rotatabl mounted armature of conductingmaterial: a magnetic member having cooperating ole faces on oppositesides of said armature or producing an alternatin flux therethrough, anenergizing win 'ng for said magnetic member, a plurality of shadingcoils on one of said pole faces arranged one within the other andenclosing different areas of said Pole faces for producing a progressiveshi ting of the flux through said armature and a magnetic shunt fordiverting flux from the area of said pole face in closed by all of saidshading coils so that it does not ass through said armature.

6. An indhction motor provided with a short circuited armature and asingle base field member having an ener 'zing po e adjacent saidarmature for pro ucing an alternating field therethrough, the pole facethereof being progressively shaded from one side to the other in thedirection of rotation and means for shunting flux from the most heavilyshaded portion of said pole face away from said armature.

7. An electric motor of the induction disc type comprising a magneticcircuit formed by a air of skeleton castings fitted together like t ebase and cover of a cylindrical box, the castings having symmetricallyarranged internal pole pieces integral with said castings and extendingtowards each other from the base and cover ture, the upper and ower polepieces being separated and aligned to form air ga s, an energizing coilfor each pair of align pole pieces, means for shifting the fluxes ofsaid pole pieces within the air gaps, a vertical shaft rotatably mountedin the center of said structure, and a disc of conducting material onsaidshaft extending into said air CHESTER I. HALL;

ositions of the struca

